The present invention relates to an image frame generating method, and more particularly to a method for digitally generating a diversified image frame.
Conventionally, an image frame is a 3:4 rectangle formed by a plurality of horizontal image signal-lines. The horizontal image signal-lines have a plurality of pixels respectively. For example, the VGA specification provides a image consisting of 480 horizontal image signal-lines. Each horizontal line has 640 pixels. Normally, such a specification is indicated as 640(H)xc3x97480(V). An object can be scanned to generate a digital image of the object. The digital image can be outputted through an electrical projector to a display such as a liquid crystal display or a monitor. The electrical projector may be a cathode ray tube (CRT), which generates the scan lines. Referring to FIG. 1, the object is scanned by the optical sensor of the scanner to generate an analog image signal (Step S11). Then, the analog image signal is converted to a digital image signal by an analog to digital converter in Step S12. In Step S12, the digital image signal is stored in a memory unit. Finally, in Step 14, the digital image signal is converted by a digital to analog converter and outputted to the electrical projector.
The electrical project will then generates an image frame as shown in FIG. 2(a). However, sometimes there may be an error in the projecting angle of the electrical projector. Accordingly, a keystone frame as shown in FIG. 2(b) or FIG. 2(c) may be generated because of the different optical path of the scan lines. Referring to FIG. 2(a), the normal image frame will have a rectangular shape wherein the dots A, B, C and D are located at the four corners of the rectangular frame. If the image is projected at an elevated angle, the frame will become a keystone shape as shown in FIG. 2(b). The scan line between upper dots B1 and C1 has a length larger than that of the scan line between lower dots A1 and D1 because the upper dots have optical paths longer than those of the lower dots. Of course, if the image is projected at an angle of depression, the image frame will be a keystone shape as shown in FIG. 2(c). The scan line between the lower dots A2 and D2 will be longer than that between dots B2 and C2 because of a longer optical path.
To avoid the undesired keystone image frame, an optical set is mounted in front of the electrical projecting device to correct the projecting angle of the image. However, to add stitch an optical set is very expensive. Furthermore, the optical set will occupy a certain volume. Therefore, the overall projecting system cannot be scaled down if such an optical set is mounted. Another method for correcting the keystone image frame is needed.
Furthermore, the conventional method for correcting the keystone frame can only perform a symmetric correction. Accordingly, a method which can not only correct the keystone frame but also diversify the outline of the image frame is desirable.
It is then attempt by the present invention to solve the abovementioned problem.
An object of the present invention is to provide a method for generating a diversified-shaped image frame.
Another object of the present invention is to provide a method for correcting a keystone projecting-image frame without needing of an expensive optical set.
A further object of the present invention is to reduce the size of an electrical projecting device.
The present invention provides a method for generating a diversified-shaped image frame formed by a plurality of image signal lines. The method includes steps of determining a specific pixel frequency of one of the plurality of image signal lines, and outputting said one image signal line according to said specific pixel frequency. The steps are repeated until all of said plurality of image signal lines are outputted.
The pixel frequency is preferably a dot clock frequency of said one image signal line. The dot clock frequency is preferably generated by a phase lock loop (PLL) technique and a frequency divider.
The plurality of image signal lines are preferably horizontal image signal lines.
The method preferably further comprising steps of adding a plurality of black pixels to the two ends of the image signal line when outputting image signal lines. When outputting the image signal line and the black pixels added beside the image signal line, a logic control technique is preferably used for switching between the black pixels and the image signal line.
The image frame may include n image signal lines. I3kxe2x88x922, I3kxe2x88x921 and I3k are the pixels added beside one end of the kth one of the image signal lines, the kth one of the image signal lines and the pixels added beside the other end of the kth one image signal lines respectively. Steps for determining the specific pixel frequency may include calculating the total pixel number of (I3kxe2x88x922+I3kxe2x88x921+I3k) and calculating and outputting the specific pixel frequency, wherein the specific pixel frequency is equal to the total pixel number of (I3kxe2x88x922+I3kxe2x88x921+I3k) divided by a duty cycle of a horizontal image-synchronous-signal of the kth image signal line, wherein n and k are positive integers and 1xe2x89xa6kxe2x89xa6n.
The plurality of image-signal lines are outputted by an electrical projecting device with an projecting angle xcex8. Accordingly, the method for calculating the total pixel number may include inputting a value of the projecting angle xcex8, inputting values of geometrical variance coefficients xcex4k1 and xcex4k2, calculating the pixel numbers of I3kxe2x88x922 and I3k, inputting the pixel number of I3kxe2x88x921, and summing up the pixel numbers of I3kxe2x88x922, I3kxe2x88x921 and I3k for obtaining the total pixel number. The pixel numbers of I3kxe2x88x922 may be equal to (nxe2x88x92k+1)xc3x97tan xcex8+xcex4k1, and the pixel numbers of I3k may be equal to (nxe2x88x92k+1)xc3x97tan xcex8+xcex4k2.
There may have another method for calculating I3kxe2x88x922 and I3k. In this case, I3kxe2x88x922=nxc3x97tan xcex8xe2x88x92mod(k/D), and I3k=nxc3x97tan xcex8xe2x88x92mod(k/D), wherein D=mod(tan xcex8).
Once the specific pixel frequency has been calculated, the image signal line may be outputted through the following steps: generating a horizontal projecting-image synchronous-orientation signal of the kth image signal line according to the horizontal image-synchronous-signal of the kth image signal line, outputting I3kxe2x88x922 according to the horizontal projecting-image synchronous-orientation signal of the kth image signal line, the specific pixel frequency and the pixel number of I3kxe2x88x922, finishing outputting I3kxe2x88x922, and outputting I3kxe2x88x921 according to the specific pixel frequency and the pixel number of I3kxe2x88x921, finishing outputting I3kxe2x88x921, and outputting I3k according to the specific pixel frequency and the pixel number of I3k, and finishing outputting I3k. Preferably, an ending signal is provided for finishing outputting I3kxe2x88x922 to output I3kxe2x88x921, an ending signal is provided for finishing outputting I3kxe2x88x921 to output I3k, and an ending signal is provided for finishing outputting I3k to output the next image signal line.
The present invention may best be understood through the following description with reference to the accompanying drawings, in which: